1. Field of the Invention
The present invention relates to a printing apparatus capable of specifying the color material concentration in ink near the orifices of the printhead.
2. Description of the Related Art
An inkjet printing apparatus prints an image by repeating a main scanning operation of discharging ink from each orifice of the printhead while scanning the printhead in the main scanning direction and a conveyance operation of conveying a print medium such as a paper sheet in the sub-scanning direction perpendicular to the main scanning direction. Inks used in the inkjet printing apparatus are roughly classified into pigment inks and dye inks. There are inkjet printing apparatuses using only pigment inks, those using only dye inks, and those using both dye inks and pigment inks in accordance with the application purpose.
Each pigment ink or dye ink is contained in an ink tank serving as a container. When the ink tank is connected to the printhead, the ink can be supplied to the orifices serving as the ink discharge unit of the printhead. There is also an ink-tank-integrated printhead having an ink tank for storing inks. In this printhead, the ink tank communicates with the orifices and supplies the inks to the orifices.
The period (e.g., physical distribution period) until an ink tank or an ink-tank-integrated printhead is attached to an inkjet printing apparatus is variable. For this reason, ink in the ink tank or ink-tank-integrated printhead may physically or chemically change depending on the conditions such as the length of the physical distribution period or the temperature and humidity in that period. Especially in a pigment ink, the pigment, i.e., the color material, readily increases its particle size or settles due to coagulation, and the pigment concentration in the ink may have a distribution. Even after the ink tank or ink-tank-integrated printhead is attached to the inkjet printing apparatus, the ink may have a concentration distribution depending on the conditions such as temperature and humidity, and how long the inkjet printing apparatus has been sitting idle in that period.
Ink with a concentration distribution may partially have, near the orifices, a pigment concentration more than a predetermined value. Discharge of the ink with a pigment concentration more than a predetermined value is unstable. Hence, the quality of an image printed on a print medium may degrade. Alternatively, when an orifice or an ink channel communicating with it is clogged with the ink with a pigment concentration more than a predetermined value, an ink supply failure may occur. Even a dye ink may have the same problems when the ink in the ink tank or ink-tank-integrated printhead evaporates, and a concentration distribution is generated in the dye or solvent.
Conventionally, techniques of forcibly discharging or sucking ink from orifices are known as solutions to the problem of poor print quality or ink supply failure caused by the concentration distribution in ink. These techniques of forcibly discharging or sucking ink include, e.g., preliminary discharge for discharging ink not to contribute to image printing and a recovery operation such as a suction operation of causing a suction pump to forcibly suck ink near the orifices. It is preferable to discharge or suck ink in an amount corresponding to the pigment concentration at a portion with a pigment concentration more than a predetermined value without degradation in print quality or ink supply failure caused by a small ink discharging or sucking amount or conversely without wasteful ink discharging or sucking.
An inkjet printing apparatus described in Japanese Patent Publication Laid-Open No. 2002-234196 can suck a suitable amount of ink by changing the amount of suction by a suction pump in accordance with the elapsed time after an ink tank was attached to the inkjet printing apparatus.
However, in the method described in Japanese Patent Publication Laid-Open No. 2002-234196, the inkjet printing apparatus needs to separately have a mechanism for calculating the elapsed time after an ink tank was attached to the inkjet printing apparatus. Additionally, since the concentration distribution of a pigment in ink also changes depending on the conditions such as temperature and humidity, the arrangement that specifies the pigment concentration in ink on the basis of the elapsed time may cause an error in the actual pigment concentration in the ink. If such an error occurs, degradation in print quality or ink supply failure may be caused by a small ink discharging or sucking amount, or wasteful ink discharging or sucking may be caused by a large ink discharging or sucking amount.